Abstract:

 When electrochemical energy storage systems are applied on-grid, the energy storage devices need to work under constant power(CP) conditions, which is different from the usual constant current(CC) testing methods. In order to know the performance of different kinds of energy storage devices under CP and CC testing conditions, commercial Supercapacitors, Valve Regulated Sealed Lead-acid Batteries(VRLA) and LiFePO4 batteries(LFP) were measured under CC and CP conditions at different rates respectively, with parameters such as voltage-capacity curves, capacity, energy and efficiency analyzed. It is found that the three kinds of energy storage devices revealed quite different performances. Supercapacitors exhibit excellent rate performance and high energy efficiency. There is no obvious difference between the CC and CP modes, while the energy efficiency is higher under the CP condition, which can reach its maximum at a certain rate. VRLA shows a poor rate performance and lower energy efficiency. Large current/power higher than 6 h-rate should be avoided for practical application, and the relevant parameters under power-based conditions need to be checked for correction. LFP battery has high energy density and outstanding rate performance, with quite similar performance under CC and CP conditions, exhibiting an excellent comprehensive property.

Key words: electrochemical energy storage, constant current charging and discharging, constant power charging and discharging, supercapacitor, lead-acid battery, LiFePO4 battery